Browsing by Author "Richmond, B"

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    Deposits, flow characteristics, and landscape change resulting from the September 2009 South Pacific Tsunami in the Samoan Islands
    (Elsevier Science, 2011-07-01) Richmond, B; Buckley, M; Etienne, S; Chagué-Goff, C; Clark, K; Goff, JR; Dominey-Howes, D; Strotz, L
    The September 29th 2009 tsunami caused widespread coastal modification within the islands of Samoa and northern Tonga in the South Pacific. Preliminary measurements indicate maximum runup values of around 17 m (Okal et al., 2010) and shore-normal inundation distances of up to similar to 620 m (Jaffe et al., 2010). Geological field reconnaissance studies were conducted as part of an UNESCO-IOC International Tsunami Survey Team survey within three weeks of the event in order to document the erosion, transport, and deposition of sediment by the tsunami. Data collected included: a) general morphology and geological characteristics of the coast, b) evidence of tsunami flow (inundation, flow depth and direction, wave height and runup), c) surficial and subsurface sediment samples including deposit thickness and extent, d) topographic mapping, and e) boulder size and location measurements. Four main types of sedimentary deposits were identified: a) gravel fields consisting mostly of isolated cobbles and boulders, b) sand sheets from a few to similar to 25 cm thick, c) piles of organic (mostly vegetation) and man-made material forming debris ramparts, and d) surface mud deposits that settled from suspension from standing water in the tsunami aftermath. Tsunami deposits within the reef system were not widespread, however, surficial changes to the reefs were observed. Published by Elsevier B.V.
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    Erosion, deposition and landscape change on the Sendai coastal plain, Japan, resulting from the March 11, 2011 Tohoku-oki tsunami
    (Elsevier B.V., 2020-12-12) Richmond, B; Szczuciński, W; Chagué-Goff, C; Goto, K; Sugawara, D; Witter, R; Tappin, DR; Jaffe, BE; Fujino, S; Nishimura, Y; Goff, JR
    Case studies of recent tsunami impacts have proven to be extremely useful in understanding the geologic processes involved during inundation and return flow, and refining the criteria used to identify paleotsunami deposits in the geologic record. Here, we report on erosion, deposition and associated landscape change resulting from the March 11, 2011 Tohoku-oki tsunami along a nearly 4.5 km shore-normal transect on the coastal plain near Sendai, Japan. The study area on the broad, low-relief prograding coastal Sendai plain comprised a sand beach backed by ~ 3 m high sand dunes and a forest, a wetland, the Teizan canal, agricultural rice fields, buildings and roads. Field observations focused on measurements of tsunami flow characteristics (height and direction), mapping of erosion features and assessing sediment deposition based on shallow trenches at 50–100 m spacing. Recorded tsunami inundation heights reached up to about 11 m above mean sea level within the first 500 m from the shoreline and then ranged between 3 and 5 m for the next 2 km, gradually decreasing to about 3 m close to the inundation limit. The tsunami deposit generally thinned landward from an average maximum ~ 30 cm thick sand deposit in the coastal forest to a thin mud drape several mm thick near the inundation limit. A discontinuous sand-dominated sheet was prevalent to about 2800 m from the shoreline where mud content then gradually increased further landward eventually resulting in a mud-dominated deposit ranging from 3.5 cm to a few mm thickness. The overall thinning and fining of the deposit was often interrupted by localized features that led to complex sedimentological relationships over short distances. Satellite imagery taken on 14 March 2011, 3 days after the Tohoku-oki Tsunami shows prominent foreshore incisions with 100 s + meters spacing alongshore, a foredune ridge that underwent severe erosion and development of a prominent shore-parallel elongated scour depression. Our field survey in early May 2011 revealed that the foreshore recovered quickly with rapid post-tsunami sediment deposition from incident waves, whereas the dune–ridge complex had undergone only minor re-working from eolian processes. © 2020 Elsevier B.V
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    Initial field survey report of the 2011 East Japan Tsunami in Sendai, Natori adn Iwanuma Cities
    (UNESCO-IOC, 2011-07-10) Sugawara, D; Goto, K; Chagué-Goff, C; Fujino, S; Goff, JR; Jaffe, BE; Nishimura, Y; Richmond, B; Szczuciński, W; Tappin, DR; Witter, R; Yuliento, E
    The East Japan Earthquake (Mw 9.0) and associated tsunami struck the Pacific coast of eastern Japan on March 11th, 2011 at 2:46 p.m. (Japan Standard Time). Maximum run-up heights reached about 40 m along the Sanriku region’s coast and around 10 m on the Sendai coastline. The coasts of Iwate, Miyagi and Fukushima Prefectures in particular were badly damaged, and a considerable amount of time and money will be required to restore these areas. Tsunami inundation up to 5 km inland occurred across the Sendai Plain, which remained partly flooded for several weeks after the event. Some areas were still under water 2 months after the earthquake, and are likely to remain flooded for some time as a result of subsidence. The Disaster Control Research Center at Tohoku University conducted scientific research of the inundated coastal plains of Sendai, Natori and Iwanuma Cities in collaboration with other research institutes from Japan and overseas with the support of UNESCO-IOC (Intergovernmental Oceanographic Commission). Data and samples collected during the field survey are now being analyzed by various institutes around the World. This report is a summary of our field survey that focused on an area to the north of Sendai Airport. Radioactivity data recorded at the time of survey are also provided.
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    Modern and possible paleotsunami deposits in Samenoura, Sanriku Coast, and their relation to tsunami source mechanisms
    (Japan Geoscience Union Meeting, 2014-05-02) Sugawara, D; Nishimura, Y; Goto, K; Goff, JR; Jaffe, BE; Richmond, B; Chagué-Goff, C; Szczuciński, W; Yokoyama, Y; Miyairi, Y; Sawada, C
    Samenoura is situated in the bay head of a small inlet on the Pacific coast of Oshika Peninsula, one of the nearest places to the epicenter of the 2011 Tohoku-oki Earthquake. According to the Joint Survey Group, wave heights were measured at more than 20 m near the coastline. This area was severely damaged as a result of both co-seismic subsidence and tsunami inundation. We carried out field surveys of the Tohoku-oki and paleotsunami deposits at Samenoura in March, May and October 2013. Sandy deposits laid down by the Tohoku-oki tsunami were up to 20 cm thick at locations with an elevation greater than 10 m, and were several cm thick within the forest higher up. The tsunami deposit also contained numerous shell fragments and foraminifera. Although some possible sources of the tsunami deposits can be attributed to narrow sandy beaches near the study area, the deposition of such a thick sandy deposit is more or less enigmatic, considering the steep Ria-type coastal topography.Using a gouge auger and geoslicer, we found at least two sand layers intercalated within muddy sediments. A volcanic ash layer, which corresponds to the AD 915 Towada-a tephra, was also identified from a horizon between these sand layers. The underlying sand layer was most probably laid down by the 869 Jogan earthquake tsunami, one of the large-scale events known to have affected the region. Previous studies of the Jogan tsunami have proposed several possible source models that involve an interplate thrust earthquake. Given that the local bathymetry and topography of Samenoura Bay may be sensitive to the waveform of a large-scale tsunami, paleotsunami deposits found from this area may be the key to determining the source mechanisms of events on the Sanriku Coast.In this presentation, the possible correlation of the sandy deposits with known paleotsunami events based on detailed radiocarbon dating is discussed. The hydrodynamic character and processes of tsunami sediment erosion and deposition in Samenoura Bay are analyzed using numerical modeling of both interplate and outer-rise earthquake scenarios. © Japan Geoscience Union Meeting, 2014.
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    New insights of tsunami hazard from the 2011 Tohoku-oki event
    (Elsevier, 2011-12-01) Goto, K; Chagué-Goff, C; Fujino, S; Goff, JR; Jaffe, BE; Nishimura, Y; Richmond, B; Sugawara, D; Szczuciński, W; Tappin, DR; Witter, R; Yulianto, E
    We report initial results from our recent field survey documenting the inundation and resultant deposits of the 2011 Tohoku-oki tsunami from Sendai Plain, Japan. The tsunami inundated up to 4.5 km inland but the >0.5 cm-thick sand deposit extended only 2.8 km (62% of the inundation distance). The deposit however continued as a mud layer to the inundation limit. The mud deposit contained high concentrations of water-leachable chloride and we conclude that geochemical markers and microfossil data may prove to be useful in identifying the maximum inundation limit of paleotsunamis that could extend well beyond any preserved sand layer. Our newly acquired data on the 2011 event suggest that previous estimates of paleotsunamis (e.g. 869 AD Jogan earthquake and tsunami) in this area have probably been underestimated. If the 2011 and 869 AD events are indeed comparable, the risk from these natural hazards in Japan is much greater than previously recognized. (c) 2011 Elsevier
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    The search for geologic evidence of distant-source tsunamis using new field data in California
    (U.S. Geological Survey, 2014) Wilson, R; Hemphill-Haley, E; Jaffe, BE; Richmond, B; Peters, R; Graehl, N; Kelsey, H; Leeper, R; Watt, S; McGann, M; Hoirup, DF; Chagué-Goff, C; Goff, JR; Caldwell, D; Loofbourrow, C
    A statewide assessment for geological evidence of tsunamis, primarily from distant-source events, found tsunami deposits at several locations, though evidence was absent at most locations evaluated. Several historical distant-source tsunamis, including the 1946 Aleutian, 1960 Chile, and 1964 Alaska events, caused inundation along portions of the northern and central California coast. Recent numerical tsunami modeling results identify the eastern Aleutian Islands subduction zone as the “worstcase” distant-source region, with the potential for causing tsunami runups of 7–10 m in northern and central California and 3–4 m in southern California. These model results, along with a review of historical topographic maps and past geotechnical evaluations, guided site selection for tsunami deposit surveys. A reconnaissance of 20 coastal marshlands was performed through site visits and coring of shallow surface sediments to determine if evidence for past tsunamis existed. Although conclusive evidence of tsunami deposits was not found at most of the sites evaluated, geologic evidence consistent with tsunami inundation was found at two locations: Three marshes in the Crescent City area and Pillar Point marsh near Half Moon Bay. Potential tsunami deposits were also evaluated at the Carpinteria Salt Marsh Reserve in Santa Barbara County. In Crescent City, deposits were ascribed to tsunamis on the basis of stratigraphic architecture, particle size, and microfossil content, and they were further assigned to the 1964 Alaska and 1700 Cascadia tsunamis on the basis of dating by cesium-137 and radiocarbon methods, respectively. The 1946 tsunami sand deposit was clearly identified throughout Pillar Point marsh, and one to two other similar but highly discontinuous sand layers were present within 0.5 m of the surface. A tsunami-origin interpretation for sand layers at Carpinteria is merely consistent with graded bedding and unsupported by diatom or foraminiferal assemblages. Additional studies, including age dating, grain-size, and microfossil analyses are underway for the deposits at Crescent City, Pillar Point marsh, and Carpinteria, which may help further identify if other tsunami deposits exist at those sites. The absence of evidence for tsunamis at other sites examined should not preclude further work beyond the reconnaissance-level investigations at those locations.
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    The use of boulders for characterising past tsunamis: lessons from 2004 Indian Ocean and 2009 South Pacific tsunamis
    (Elsevier, 2011-07-01) Etienne, S; Buckley, M; Paris, R; Nandasena, AK; Clark, K; Strotz, L; Chagué-Goff, C; Goff, JR; Richmond, B
    Tsunamis are high energy events capable of transporting extremely heavy loads including boulders. We compare boulder deposits created by two modern tsunami events, the 2004 Indian Ocean and the 2009 South Pacific tsunamis, where the boulder sources were in similar topographic settings, and for which we have accurate data on the wave characteristics. Boulder distribution, preferential orientation and numerical simulation of boulder transport are discussed. A comparison between the impacts of the South Pacific and Indian Ocean tsunamis shows similar characteristics, such as limited landward extent and the absence of landward fining. Differences between the results from modelling and field data are most probably caused by variables such as coastal plain roughness (buildings, trees), microtopography, particle shape, and boulder collision during transport that are summarised as coefficients in the mathematical models. Characterising modern events through coarse sediment deposits provides valuable information to help identify and interpret palaeo-tsunami imprints on coastal landscapes. (C) 2011 Elsevier B.V.
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    Using magnetic fabric to reconstruct the dynamics of tsunami deposition on the Sendai Plain, Japan — the 2011 Tohoku-oki tsunami
    (Elsevier B.V., 2014-12-01) Schneider, JL; Chagué-Goff, C; Bouchez, JL; Goff, JR; Sugawara, D; Goto, K; Jaffe, BE; Richmond, B
    The magnetic fabric and grain size of sand deposits emplaced during the 2011 Tohoku-oki tsunami were studied in five trenches along a 1800 m long shore normal transect on the Sendai plain as well as in a near shore sedimentary infill of a scour depression. The magnetic susceptibility in all deposits is due to ferromagnetic minerals (mainly magnetite) making the anisotropy of magnetic susceptibility (magnetic fabric) suitable for fabric analyses. The dominant magnetic fabric is planar in all trenches and stronger in finer-grained inland deposits than in the coarser sediments. This planar fabric is related to tractive shearing of the bedload basal portion of the tsunami flow that led to the deposition of traction carpet layers. Among the various fabric parameters used for this study, the vertical evolution of the shape factor (q) of the magnetic ellipsoid in each trench follows the evolution of the magnetic lineation (L) and foliation (F). These parameters provide information on the hydrodynamic energy (flow speed) fluctuations during the emplacement of the tsunami deposit. For the most proximal deposits, characterized by well-sorted reworked beach sand with minor fluctuations in grain-size distribution, the magnetic fabric is sensitive to hydrodynamic energy variations during sedimentation. Reconstruction of tsunami flow orientation in the sediments, based on the orientation of the mean Kmax calculated for each trench, appears to be unambiguous only for the sandy infills of small topographic depressions. The variations in flow direction indicators elsewhere could be related to local variation of the flow and to micro-topographic effects. These findings are encouraging for the use of the magnetic fabric proxy in the study of paleotsunami deposits. © 2014 Elsevier B.V.